Inverters are electrical devices that typically include transformers, switches, and control circuits for converting direct current (“DC”) voltages to alternating current (“AC”) voltages, with the resulting AC voltage being at a particular amplitude (e.g., 120V or 220V) and frequency (e.g., 50 to 60 Hz). Inverters are used in portable appliances, consumer electronics, backup power supplies for telecommunication and computer installations, such as uninterrupted power supplies, or UPS, or other applications that include DC sources of power. Inverters are being used increasingly in power generation and distribution systems based on solar, wind power and fuel cell technologies to convert DC voltages (i.e., variable DC voltages) to 120/220 VAC. In one approach, some traditional “modified sine wave” inverters implement modified square waves to approximate a sinusoidal AC voltage waveform. The modified sine wave inverters, however, use square-shaped waveforms that tend to produce levels of noise that may not be suitable for motors or other applications in which sinusoidal-shaped voltages might be desired.
FIG. 1 depicts another approach to implementing conventional inverters with multiple levels, including a DC-to-DC conversion level and a DC-to-AC conversion level. Examples of some traditional inverters that have multiple levels include class-A/B and class-D inverters, whereby a raw power level is converted into a regulated DC voltage within a first level, and the regulated DC voltage is converted into AC voltage in a second level. Inverter 100 is a multiple-level inverter that includes a DC-to-DC Generator 102 coupled to a DC-to-AC Generator 152. Typically, inverter 100 uses DC-to-DC Generator 102 to boost a DC voltage (e.g., 12VDC or 24VDC) applied to input terminals 104 up to 170VDC, which, in turn, is converted into 120VAC at output terminals (“AC output”) 160 by DC-to-AC Generator 152. As shown, DC-to-DC Generator 102 includes a number of relatively large switching devices 108 to drive transformer (“T1”) 110 to step up the input DC voltage. DC-to-DC Generator 102 also includes rectifying circuits 112, a filter choke 114 and electrolytic capacitors 120. Filter choke 114 and electrolytic capacitors 120 constitute a reconstruction filter 113 in some conventional inverters. Note that DC-DC control circuit 130 controls switching devices 108 responsive to linear feedback from transformed DC voltages between filter choke 114 and electrolytic capacitors 120. Further to inverter 100, DC-to-AC Generator 152 includes a DC-to-AC control circuit 154, an H-bridge circuit 156, and a filter 158.
While functional, inverter 100 has various drawbacks in its implementation. First, DC-to-DC Generator 102 and DC-to-AC Generator 152 each include control circuits, rectifier circuits and feedback circuits, which consume resources such as semiconductor and computational resources. Second, a current path magnetically coupled from input terminals 104 to output terminals 160 may pass through five semiconductor devices (and their junctions), such as through Q3, Q2, and Q1 of switching devices 108 and through any two of the devices in H-bridge circuit 156, whereby each of the semiconductor devices in the current path dissipates power due to switching and conduction losses. Third, transformer 110 and filter choke 114 may dissipate power due to, for example, core losses and conduction losses. Fourth, the current path also passes (e.g., as ripple current) into electrolytic capacitors 120 as storage capacitors. A ripple current may cause electrolytic capacitors 120 to heat up, thereby drying out the electrolyte material. In some inverters, electrolytic capacitors 120 can be the least reliable components of inverter 100 as the mean time between failures (“MTBF”) may be 5 to 7 years, which is not uncommon for an electrolytic capacitors 120. Note that the MTBF for electrolytic capacitors 120 is typically less than the life expectancy of their intended applications (e.g., for use in solar energy generation systems). Note, too, that conduction and switching losses may be associated with rectifying circuits 112. Fifth, transformer 110 typically has multiple windings at the side coupled to rectifying circuits 112. Further, transformer 110 has an amount of windings necessary to step up a DC voltage (e.g., 12VDC or 24VDC) to 170VDC, as well as an amount of iron or core material to support the amount of windings, whereby the amount of windings and the amount of core material may contribute respectively to conduction losses and core losses.
It is desirable to provide improved techniques, systems, integrated circuits, and methods that minimize one or more of the drawbacks associated with devices, integrated circuits, substrates, and methods for convert direct current voltage signals to alternating current voltage signals.
Like reference numerals refer to corresponding parts throughout the several views of the drawings. Note that most of the reference numerals include one or two left-most digits that generally identify the figure that first introduces that reference number.